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Neo-Darwinism has failed as an evolutionary theory

22 May 1995

Darwinism is a theory of evolution based upon inherited variations in organisms and natural selection of fitter variants to produce species adapted to their habitats. Twentieth-century biology added a theory of inheritance, the science of genetics, to give Neo-Darwinism. In the past 20 years the techniques of genetics and molecular biology have converged to provide both a remarkably detailed understanding of the genes that define the molecular composition of any organism and the ability to transfer genes from one species to another.

There is no doubt about the importance of the insights that have resulted from this increased genetic and molecular focus. The problem is that the claims made for these revelations are frequently so misleading and distorted that the whole field becomes tarnished by exaggeration and real scientific problems are obscured. Biology then suffers. A widely quoted example with which many biologists agree is the description by Delisi (American Scientist) of what the human genome project will reveal about human development. "This collection of chromosomes in the fertilised egg constitutes the complete set of instructions for development, determining the timing and details of the formation of the heart, the central nervous system, the immune system, and every other organ and tissue required for life."

A colleague in the States who is a firm believer in the importance of genes in development and evolution says he uses the Delisi quotation in his developmental biology class to show the stupidity of the reductionist paradigm. So biology is a broad church that contains many points of view. But the most prominent public voices present the reductionist position. Richard Dawkins, a fervent adherent of extreme genetic reductionism, describes in The Blind Watchmaker a willow tree releasing seeds within which is the "DNA whose coded characters spell out specific instructions for building willow trees". For him the genes define the essence of life and the organism is just a survival machine built by genes for their own perpetuation. Steve Jones regards this as "the best general book about evolution since the second world war". And Lewis Wolpert delivers the same message as Dawkins: "DNA provides the programme which controls development of the embryo and brings about epigenesis" (The Triumph of the Embryo).

What is wrong with these statements is that they define scientific positions that need to be backed up by models that demonstrate precisely how a knowledge of genes in the developing organism will lead to an understanding of the three-dimensional form of the human heart or limb or eye, the arrangement of leaves on a plant and the organs of the flower, or the wings of a fruit fly. But this is not provided. The discussion always stops at the spatial patterns of gene products in developing organisms, if indeed it gets even that far. The crucial step of generating the actual three-dimensional structures that characterise the distinctive morphology of species is left unexplained.

To understand why organisms look the way they do we need models that involve physical forces as well as biological variables, organised to produce organisms with specific morphologies, as described in my book, How the Leopard Changed its Spots. To say there is a program in DNA that constructs the organism is to use a misleading shorthand or to fail to understand the problem. It is like saying that all you need to know to understand high-temperature superconductors is what they are made of and where the atoms are relative to one another. Try that on a physicist. And organisms are at least as complex as superconductors. Yet we are constantly being told that molecular analysis will reveal all. The rhetoric here frequently overwhelms the science, which is doubly unfortunate: the science is sufficiently exciting in its own right and does not need the hyperbole, while the problems it cannot address are being neglected.

Nowhere is this more evident than in the claim that Neo-Darwinism explains evolution. Evolution is about the origin of species, the emergence of new types of organism characterised by distinctive morphologies and behaviours. This requires a theory of organisms as life-cycles, including morphogenesis (how organisms of specific form are generated) and of their interactions with one another and the physical environment in producing communities and ecosystems. But far from concentrating on the development of theories of organisms and ecosystems, Neo-Darwinism concentrates on genes as the fundamental entities in biology.

This cannot succeed because it leaves out too much. Organisms are large-scale physical systems that grow and develop, run, fly, produce leaves and flowers, and generate patterns of relationships with each other. Some of them even love and write poetry. Genes do none of these things, and neither do molecules.

Neo-Darwinism has failed as an evolutionary theory that can explain the origin of species, understood as organisms of distinctive form and behaviour. In other words, it is not an adequate theory of evolution. What it does provide is a partial theory of adaptation, or microevolution (small-scale adaptive changes in organisms). It is partial in two senses. First, Neo-Darwinism assumes random genetic variation followed by selection, whereas there is now evidence for a role of directed mutation in adaptive response. That is, genes can evidently respond to environmental circumstances by non-random, adaptive mutation. And second, many of the adaptive "explanations" advanced for biological characteristics simply cannot be taken as serious science. In 1979, Steven Jay Gould and Richard Lewontin published a classic paper that ridiculed much of the adaptationist literature as constituting a "panglossian paradigm", Just So Stories of such dubious scientific value that they discredit the subject. For a few years after that, adaptationists watched their p's and q's more closely. However, the salutary influence of that paper has unfortunately diminished to the point where Just So Stories are again proliferating wildly. A recent example is why the hour-glass shape in women is an adaptive trait, determined by genes. Men select women with large hips and breasts because these are indicators of reproductive potential, or at least men think they are. Women who satisfy these criteria but do not have a small waist are simply fat, which, we are told, is not a good indicator of reproductive potential. Hence the selection of the hour-glass shape. You might think I overheard this in a pub, but it is in fact advanced as a serious proposition by Matt Ridley in The Red Queen following the original proposal by Low, Alexander, and Noonan in Ethology and Sociobiology. If this is science then Rudyard Kipling was a great scientist.

Adaptation is an important problem, but it is not the same as evolution. Still less is it the same as macroevolution, which is about large-scale evolutionary change: the emergence of algae, mosses, ferns, grasses, flowers, trees; of protozoa, sea urchins, octopus, fish, amphibia, birds, mammals. For these qualitative changes, the stuff of evolution, there is no adequate theory. A primary reason for this absence is the narrative style that has been adopted within biology since Darwin's re-description of the subject as an historical science. Species have come to be seen as individuals, the results of historical contingencies, so that the morphological relationships between species have become unintelligible because they are accidental, not necessary. And yet there is plenty of evidence for a deep level of structural order that underlies the taxonomic regularity of the biological realm, the systematic similarities and differences of species. This is the level of structural constraint that Gould and Lewontin were reminding us of: biological form cannot be explained away in functional (adaptational) terms, nor is any form possible. There is a long tradition in biology of seeking to understand this intrinsic order in terms of a theory of biological form and transformation that is now re-emerging from more sophisticated non-linear dynamic modelling of morphogenesis and a deeper understanding of the causal mechanisms involved.

It is clear biology needs a theory of organisms as self-organising systems that generate emergent order if evolution is to be understood. This is now a very real and exciting possibility, but it is an interdisciplinary task that requires mathematical, physical, and biological input. It simply cannot come from the study of genes and molecules alone, useful as this is.

There is another dimension of Neo-Darwinism that is also problematic. The analytical power of molecular genetics has resulted in a new expansion of Neo-Darwinism with a strongly applied, technological dimension. One manifestation of this is the project to identify every human gene, coordinated by the international Human Genome Organisation (HUGO), with associated squabbling over patent rights on potentially lucrative applications in the fields of medicine and designer gene engineering. The French geneticist Daniel Cohen has led the movement to have this information recognised by the United Nations as the property of humanity to use freely for any appropriate purpose. But 17 companies are now in a position to patent many of the 100,000 genes of the human body so that, unless patent rights are paid for use, they can withhold the information that would otherwise be valuable for medical research.

There are immense social and ethical issues involved. It is obvious extreme caution is required because of our ignorance of the genetic, biological, and ecological consequences of gene manipulation. Any applications should be governed by principles such as no use of the technology unless there is a clearly demonstrated need, extensive testing of safety before any application, and establishment of rigorous safety protocols on international movements of transgenics and their use in the field. There is a call for a moratorium on the large-scale release of genetically engineered organisms into the environment until such safety protocols have been put in place. Without this, we shall find that Neo-Darwinism is not only prone to misleading rhetoric and inadequate science, but its applications may result in ecologically dangerous agricultural applications.